The invention relates to a process for preparing an ethylene amine mixture by hydrogenation of an amino nitrile mixture over a catalyst, in which the amino nitrile mixture is prepared from crude AAN. The individual ethylene amines can, if appropriate, be isolated from the ethylene amine mixture obtained.
It is generally known that nitriles can be hydrogenated in the presence of catalysts to give the corresponding amines. Depending on the reaction parameters chosen, the known processes give the desired products, for example primary amines as main product and secondary and tertiary amines as by-products. A problem here is often that the desired product is obtained with lower selectivity and/or in lower yield, frequently also accompanied by rapid deactivation of the catalyst used.
In addition, it is known that in processes for preparing amines by hydrogenation of nitriles a certain proportion of ammonia improves the selectivity of the hydrogenation to primary amines and suppresses the formation of secondary and tertiary amines. However, hydrogenation in the presence of ammonia involves an additional engineering outlay associated with separation of the ammonia from the product stream, the work-up and possible recirculation of the ammonia. In addition, higher pressures can be required in the hydrogenation, since the partial pressure of the ammonia has to be taken into account.
Thus, ethylenediamine (EDA), which is a starting material for, for example, the synthesis of complexing agents or bleach activators which are used, inter alia, as additives for laundry detergents or cleaners, can be prepared as main product by hydrogenation of aminoacetonitrile (AAN). The hydrogenation of iminodiacetonitrile (IDAN) analogously gives diethylenetriamine (DETA) as main product. However, the hydrogenation of AAN or IDAN also always gives DETA or EDA, respectively, as by-products.
DE-A 3 003 729 describes a process for the hydrogenation of aliphatic nitriles, alkylene oxy nitriles and alkylene amino nitriles to primary amines over a cobalt or ruthenium catalyst in the presence of a solvent system. The solvent system used comprises water and ammonia together with an ether or polyether which preferably has from 4 to 6 carbon atoms and a carbon to oxygen ratio of from 2:1 to 5:1, e.g. dioxane, tetrahydrofuran, methylene glycol dimethyl ether or diethylene glycol dimethyl ether, with cyclic ethers such as dioxane and tetrahydrofuran being particularly preferred. As nitrile component, particular preference is given to dinitriles. However, DE-A 3003 729 does not disclose that compounds having both a cyano group and an amino group in the α position, e.g. AAN, can also be used in the process.
EP-A 0 382 508 describes a process for the batchwise preparation of acyclic, aliphatic polyamines by hydrogenation of acyclic, aliphatic polynitriles in the liquid phase over Raney cobalt catalysts, preferably in the presence of anhydrous ammonia. Here, a polynitrile solution is fed into a reaction zone which comprises the Raney cobalt catalyst in an essentially oxygen-free atmosphere. During the entire reaction time, the polynitrile solution is fed in at a rate which is not greater than the maximum rate at which the polynitrile reacts with the hydrogen in the reaction zone. A reaction parameter K which is suitable for determining the volume feed rate is also mentioned. The process described is restricted to the preparation of polyamines from polynitriles such as iminodiacetonitrile (IDAN), nitrilotriacetonitrile (NATN) or further compounds having 2 or more cyano groups. However, the reaction of compounds having one cyano group, e.g. AAN to EDA, is not described.
EP-A 212 986 relates to a further process in which aliphatic polynitriles can be hydrogenated over a granular Raney cobalt catalyst in the presence of a liquid primary or secondary amine comprised in the feed stream to give the corresponding polyamines. Mention is made of, inter glia, the amino component EDA which always has to be present and also numerous further primary or secondary amines. Furthermore, this document specifically discloses that IDAN can be hydrogenated to DETA.
DE-A 1 154 121 relates to a process for preparing ethylenediamine in which the starting materials hydrocyanic acid, formaldehyde, ammonia and hydrogen are reacted in the presence of a catalyst in a one-pot process. Both the ammonia and the hydrogen are used in a molar excess over the further starting materials hydrocyanic acid and formaldehyde which are present in equimolar amounts. In this process, the AAN formed in situ is thus not isolated but directly reacted further with hydrogen. A disadvantage of this process is that the desired product (EDA) is obtained relatively unselectively in small amounts.
U.S. Pat. No. 3,255,248 describes a process for the hydrogenation of organic nitrogen-carbon compounds, which preferably have amino groups substituted by nitro, N-nitroso, isonitroso or cyano groups or by aromatics, to the corresponding amines in the liquid phase using a sintered catalyst comprising cobalt or nickel. Here, the starting material is sprinkled either alone or in the presence of a solvent, for example water, tetrahydrofuran, methanol, ammonia or the reaction product formed, together with the hydrogen onto the catalyst. If compounds which are unsaturated at the nitrogen atom, e.g. cyano groups, are hydrogenated, the presence of ammonia in the reaction is recommended. This is made clear in Example 1 of this patent, where aminoacetonitrile is sprinkled in the form of an aqueous solution together with liquid ammonia but without another solvent onto the sintered catalyst. The pressure used was 280 atm.
EP-A 1 209 146 relates to a further process for the continuous hydrogenation of nitriles to primary amines, in which the respective nitriles are used in the liquid phase over a suspended, activated Raney catalyst based on an alloy of aluminum and the reaction is carried out in the absence of ammonia and basic alkali metal or alkaline earth metal compounds. Among many others, AAN and IDAN can be used as nitriles in the reaction to form the corresponding ethylene amines. If appropriate, the nitrile to be hydrogenated can also be present in solution in an organic solvent, preferably an alcohol, amine, amide, in particular N-methylpyrrolidone (NMP) and dimethylformamide (DMF), or an ether or ester. However, EP-A 1 209 146 gives no indication that IDAN and AAN can be hydrogenated jointly.
Thus, none of the prior art reports that mixtures of amino nitriles which comprise IDAN and AAN can also be hydrogenated. Rather, the processes of the prior art are restricted to the hydrogenation of individual substances.
Processes for preparing AAN and IDAN are likewise known. Thus, U.S. Pat. No. 5,079,380 relates to a process for preparing AAN, in which ammonia (NH3), formaldehyde (HCHO) and hydrocyanic acid (HCN) are reacted at at least 100° C. It is also generally known that, as an alternative, formaldehyde and hydrocyanic acid can firstly be reacted to form formaldehyde cyanohydrin (FACH) as intermediate which is subsequently reacted with ammonia to give AAN. The molar ratio of ammonia to FACH or to formaldehyde and hydrocyanic acid is usually ≧4:1 [mol/mol]. The temperatures in the AAN synthesis are in the range from 50 to 80° C. and the pH is about 10. To be able to prepare IDAN, ammonia and FACH or ammonia, formaldehyde and hydrocyanic acid are likewise typically used as starting materials. The reaction to form IDAN is generally carried out at higher temperatures (about 100-150° C.), a lower pH of about 5-7 and a smaller proportion of ammonia than in the corresponding synthesis of AAN. Such processes for preparing IDAN are described, for example, in EP-A 426 394 or U.S. Pat. No. 4,895,971. As an alternative, the preparation of IDAN can also be carried out by reaction of urotropin (hexamethylenetetramine; HMTA) with hydrocyanic acid and formaldehyde, as described, for example, in U.S. Pat. No. 3,988,360.
U.S. Pat. No. 2,511,487 relates to a process in which IDAN is prepared from AAN. Here, AAN is mixed with FACH in a molar ratio of about 1:0.3-1.5 [mol/mol] and heated to from 100 to 150° C. in the presence of a mineral acid stabilizer such as phosphoric acid. To obtain a very high yield of IDAN, the reaction preferably takes place at from 135 to 150° C. and for a maximum of 15 minutes. The process described in U.S. Pat. No. 2,511,487 takes place in a conventional flask with cooling facilities.
It is therefore an object of the invention to provide a simple and inexpensive process for preparing the ethylene amines EDA and/or DETA. The process should achieve a high conversion at a high selectivity, with the ratio of DETA to EDA being able to be varied and set specifically.